Electromagnetic horns



Julyv 15, 1969 J. DOUGALL 3,456,254

ELECTROMAGNETIC HORNS Filed Aug. 13, 1965 United States Patent O 3,456,254 ELECTROMAGNETIC HORNS John Dougall, Birmingham, England, assignor to Joseph Lucas (Industries) Limited, Birmingham, England, a British company Filed Aug. 13, 1965, Ser. No. 479,594 Claims priority, application Great Britain, Aug. 28, 1964, 35,455/ 64 Int. Cl. Gk 9/14; G08b 3/10 U.S. Cl. 340-388 1 Claim ABSTRACT OF THE DISCLOSURE This invention relates to electromagnetic horns of the kind comprising a casing which supports an electromagnet for reciprocating a diaphragm.

A diliiculty with such horns is that if the casing is sealed with enamel and then stoved, the tuning of the horn is upset because the air inside the casing escapes while the enamel is still liquid, and cannot reenter the casing when the enamel has set. The tuning cannot then be altered without breaking the seal. The object of the invention is to minimize this diiculty.

According to the invention, a horn of the kind specified includes a .resilient sealing member on the exterior of the casing and forming a sealed enclosure with a part of the horn in which is formed a hole.

The accompanying drawing is a cross-sectional view of an electromagnetic horn according to one example of the invention.

Referring to the drawing there is provided a horn having a cylindrical casing 10 which at one end is formed with a neck 11, of reduced cross-section, the neck 11 being closed at one end but formed with a central plunged hole so as to define an axially extending integral sleeve 12. Located within the neck 11, is an electromagnet 13, the pole piece 14 of which is in screw threaded engagement with the sleeve 12.

The other end of the casing 10 is formed with an outwardly extending peripheral flange 15 to which is secured a diaphragm 16 closing the casing. Rigidly secured to the diaphragm 16 is the armature 17 of the electromagnet 13, the armature extending axially within the casing 10 to a position spaced from the pole piece 14. The armature 17 is formed with an extension 18, which passes through the diaphragm, and to which is secured a tone plate 23.

When the electromagnet is energized, the armature 17 is drawn towards the pole piece 14 against the resilience of the diaphragm 16. As the armature moves towards the ICC pole piece 14, a washer 21 opens a pair of contacts 22 in the casing, thereby -breaking the circuit to the electromagnet and allowing the armature to return to its original position under the action of the diaphragm 16. The contacts 22 then close and the cycle is repeated so that the diaphragm is reciprocated to produce a sound.

The pole piece 14 is adjusted relative to the sleeve 12 to a position such that the armature 17 strikes the pole piece 14 as the contacts 22 are opened, so that the tone plate 23 produces a note which blends with the note from the diaphragm to produce the sound of the horn. After adjustment, the pole piece is fixed in position for example by soldering.

The neck 11 is formed with a hole 24 in its end face, and enclosing the neck 11 is a bellows 25 which closes the hole. In an alternative arrangement (shown in dotted lines) the hole 24 is formed in a cylindrical wall of the casing 10 the exterior of the wall then being surrounded by a resilient annular sleeve 26 of channel shaped crosssection. Both arrangement ensure that when the casing is coated with enamel and stoved, air in the casing can expand without escaping from the casing, so that the tuning of the horn is unaifected by the stoving operation. Moreover, in use the horn is completely sealed and waterproof and is unaffected by temperature changes. The arrangement using the bellows is preferred, Ibecause the bellows always reassumes its original shape, so that a batch of horns will all be similar in appearance.

Having thus described my invention what I claim as new and desire to secure my Letters Patent is:

1. An electromagnetic horn assemblage comprising a casing having a neck portion of lesser cross-section and an open end, a diaphragm secured to the casing closing the open end, an electromagnet mounted within the neck portion including a pole piece and an armature extending axially of the casing with said pole piece and armature being spaced apart, said armature having an extension passing through such diaphragm, a flange on the armature, a tone plate secured to said extension, a pair of contacts within the casing so that upon energization of the electromagnet, the armature is drawn toward said pole piece and said flange opens said contacts breaking the circuit to the electromagnet whereby the diaphragm returns the armature to its original position and said contacts close, said neck portion having a through aperture therein, and a bellows carried by said neck portion enclosing said aperature whereby air within the enclosure dened by the diaphragm and neck portion can expand via said aperature and bellows without escaping from the assemblage.

References Cited FOREIGN PATENTS 308,629 3/ 1929 Great Britain.

THOMAS A. ROBINSON, Primary Examiner U.S. Cl. X.R. 340-387 

